Main landing gear having tilting of main gear pivot pins

ABSTRACT

A main landing gear system which employs Ackermann type steering utilizing kingpins and tierods wherein a plurality of paired wheels are employed and wherein each truck axle is adapted for independent steering. Electronic control means along with hydraulic directional valve means are utilized. A main landing gear having single wheel or king pin steering. Pivot pin tilting is utilized in truck type main landing gear, e.g. where a truck axle is adapted for independent steering or where single wheel or king pin steering is utilized.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation-in-part of prior application numberU.S. Ser. No. 08/214,483, filed Mar. 17, 1994, now abandoned, alsoassigned to the Boeing Company.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to aircraft steerable main landing gear orsingle wheel or ring pin steering in which pivot pin tilting isutilized.

2. Description of the Prior Art

In the patent literature, U.S. Pat. No. 2,567,074 to Kupiec; U.S. PatNo. 2,682,311 to Bishop; and U.S. Pat. No. 3,516,625 to Hauser, et al.are illustrative of steering which is accomplished by pivoting theentire truck about a vertical axis as a single unit. Control of relativerotation between trucks is accomplished by a variety of means in thesesystems.

U.S. Pat. No. 2,630,285 to Geisse shows a means of coupling pairs ofwheels on a common axis using kingpins and tierods. Systems are shownfor both single and multiple axle landing gear trucks. In contrast tothe present system, castered wheels are shown for self alignment. Thereis no mechanism for steering the wheels.

Great Britain Patent No. 904,783 is exemplary of load equalizationtechniques wherein there is shown wheel truck where wheel pairsarticulate about a longitudinal axis so as to equalize wheel loads whenan aircraft encounters transverse terrain contours.

U.S. Pat. No. 4,917,334 to Ralph et al. shows a multi-wheeled trailingtype landing gear. In this configuration, the forward axle (2 wheels) ismounted directly to the shock strut. The aft two axles, 2 wheels each,are mounted on a truck which is cantilevered from the aft side of thestrut on a pivoting radius arm. Shock absorbers are used to react thevertical loads. This is in contrast to the present load equalizationwhere a primary truck is pivoted on the shock strut, and secondarytrucks are pivoted on the ends of the primary strut.

As aircraft get progressively larger, wheels per landing gear (and/orgears per aircraft) increase the amount in order to offset the problemin flotation and tire loading limitations.

However, as the number of wheels and gears increase, so does thereluctance of the main landing gear to allow the aircraft to turn duringsteering.

The main landing gears increasing adhesion to the ground (tracking)causes a reduction adhesion to the ground at the nose gear. When theground adhesion at the nose gear approaches zero, the directionalcontrol of the aircraft during taxi is greatly decreased.

During tractor towing operations, the nose gear steering angle isgoverned by the tractor but heavy torsional loads can be induced intothe main landing gears resulting in heavy designs.

The above problems have resulted in the incorporation of the "body gearsteering system". However, without the advantage of load equalizationthe turning moments due a one tire flat situation, are reacted by thesteering actuators. This results in exceptionally large and heavyactuators.

Problem

Unlike most nose landing gears, main landing gear with steeringcapabilities do not have a "mechanical trail" which enables thewheel/wheels to self-center in the event of hydraulic system orcomponent failure. This mechanical trail is the distance between thecenter of tire contact area on the ground and center of the steeringaxis. Heretofore, there has been no main landing gear with steeringcapability which would return to center (or the "straight ahead mode")without the assistance of some independent force.

SUMMARY OF THE INVENTION

The correct angulation to a vertical of main gear steering pins couldprovide the tendency for the already steered wheels to veer back to afore/aft attitude in the unlikely event of a component or systemfailure. This angulation is equivalent to driving the wheel uphillduring the initial steering operation, and free wheeling downhill onreturn to center.

In the case of the single wheel (or king pin) steering, the pins wouldbe vertical when viewed from the side elevation, and when viewed from afore/aft elevation, the tip of the pins would lean outboard and lowerend would obviously point inboard.

Similarly, rear axle steering could benefit from this application ofthis system concept, except that is this further embodiment two wheelsare joined with a single axle and therefore the inclination of the pinwould be different. The single pin is vertical when viewed from afore/aft elevation, and the top of the pins lean forward (the lowerportion of the pin would point to the rear) when viewed from a sideelevation. This would also hold true for the front axle, and for anyaxle which has a steering requirement.

BRIEF DESCRIPTION OF THE DRAWING(S)

FIG. 1 is a plain view illustrative of Ackermann system components forpaired wheels on a truck axle;

FIG. 2 is a view as FIG. 1 however looking forward and showing a flattire;

FIGS. 3A, 3B and 3C are descriptive and illustrative of the problem ofwheel load equalization in multi axled landing gear;

FIGS. 3D, 3E, 3F and 3G are illustrative of the solutions to theproblems shown in FIGS. 3A, 3B and 3C;

FIGS. 4A, 4B and 4C utilize the arrangement of FIG. 1 utilized forsteering a 4 wheeled truck;

FIGS. 5A, 5B and 5C incorporate the steering arrangement of FIG. 1,however applied to a 6 wheeled truck;

FIG. 6 is illustrative of a Boeing 747 type aircraft body gear;

FIG. 7 is illustrative of the present single wheel steering main landinggear system;

FIGS. 8A, 8B, 8C and 8D show steering arrangements for steering an 8wheeled truck utilizing the present single wheel steering main landinggear systems concept;

FIG. 9 is illustrative of how the present single wheeled system can beutilized in a 8 wheeled truck to offset the effect of a side driftlanding;

FIG. 10 while representative of an improbable but if practicalconfiguration relating to the near elimination of pivoting loads; and

FIG. 11A is illustrative of axle steering when viewed in the fore/aftdirection;

FIG. 11B is a side view illustrative of the axle steering of FIG. 11A;

FIG. 12A is a side view illustrative of single wheel steering whenviewed in the fore/aft direction; and

FIG. 12B is a side view illustrative of single wheel steering whenviewed in the fore/aft direction.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

A main landing gear steering system which uses the "Ackermann SteeringSystem" (Automotive type with kingpins and tierods). Each truck axle isa candidate for independent steering, depending on the amount of controldesired. When combined with electronic control of hydraulic directionalvalves, the axles can be turned in opposite directions to give minimumturning radius, or all turned the same direction to compensate for aside drift landing, or any combination in between.

Current landing gears do not provide independent steering of each axleon multiple axle trucks. This limits the minimum turning radius of theaircraft and induces large loads on the truck structure, thus requiringcorrespondingly heavy construction. This invention as exemplified in theembodiments hereinafter described is directed to a main landing gearsteering concept which employs Ackermann type steering which employskingpin and tierods wherein a plurality of paired wheels are employedand wherein each truck axle is adapted for independent steering.

The term "single wheel steering" where utilized in the followingdescription relates to main gears having a minimum of two wheels (twin)as shown, for example, in the embodiment of FIGS. 1 and 2.

The present main landing gear single wheel steering system reacts to allmovements due to a brake drag and side loads provided these loads areequally distributed between the two wheels.

Small, unequal movements due to unequal tire pressures or otherincidental rolling friction variations can be accommodated by thesteering acuator.

Large, unequal movements due to "one burst tire case (see FIG. 2)" andsmall deviations in frictional coefficients can be minimized by the useof the load equalization system solutions of FIGS. 3D, 3E, 3F and 3G.Such usage of load equalization in the present main landing gear singlewheel steering systems is an option which could reduce reaction on thesteering actuator by e.g, 80 percent.

Turning now to FIG. 1, a plan view of a first embodiment of the presentinvention can be seen in which a main gear truck 20 having two wheels 24comprises further a bell crank 26 with vertical pin 28 per wheel, eachbell crank 26 being connected symmetrically with a tie rod 30. Steeringactuator 32 is coupled between bell crank 26 and main gear truck 20 bymeans of vertical pin 28. The forward direction is represented by arrow40 and drag forces by arrows 42. This main landing gear single wheelsteering system reacts to all movements due to brake drag and side loadsprovided these loads are equally distributed between two wheels 22 and24. Small unequal movements due to unequal tire pressures or otherincidental rolling friction variations can be accommodated by steeringactuator 32.

Apart from the "one burst tire" case shown in FIG. 2 and smalldeviations in frictional coefficients, the movements about vertical pins28 are equal and opposite. Each pin 28 is located in a bell crank 26which are then connected symmetrically with a tierod 30 by means of atensile load, a steering system used and known in the automobileindustry as the "Ackermann" steering system. With the aforementionedconditions of small deviations in frictional coefficients, the load inactuator 32 would only be that required to move wheels 22 and 24 to therequired steered position.

However, in the case of a flat tire (FIG. 2) wheel load equalizationsuch as shown in FIGS. 3D, 3E, 3F and 3G must be used to enable thewheel rim (in the absence of the blown tire) to contact the ground. Thismaintains as much as possible the movement created by the rollingresistance of the tire prior to blowing. Any difference in rollingresistance of an unblown tire (24 in FIG. 2) and a wheel rim (tire 22side in FIG. 2) will increase the steering actuator accordingly, "rollon rim" requirements however tend to keep this increase to a minimum.

Turning now to the wheel load equalization problem, it can beappreciated that due to depressions and humps in the surface of runwaysit is difficult to achieve equal loading of wheels associated withmulti-axled landing gears. Equal loading in a fore and aft direction for3 or 4 wheeled trucks is achieved as shown in FIG. 3A.

For trucks consisting of 5 (or more) wheels, load equalization cannot beachieved completely by the single continuous truck beam as shown in FIG.3B.

Equal loading in the transverse direction is not achievable onconventional wheel axles as shown in FIG. 3C. This statement applies toall landing gears having twin type multi-axles. Note:

The problem of unequal loading is less with landing gears having 4 (orless) wheels,

The deflection has a beneficial effect,

The problem becomes an issue with landing gears having 5 (or more)wheels,

Unequal tire loading would adversely affect brake performance, tirewear, and fatigue life of related component parts.

FIGS. 3D, 3E, 3F and 3G show proposed solutions to the problem of loadequalization.

(a) Load Equalization--Fore and Aft Direction

FIGS. 3E and 3F illustrate the arrangement of multiple truck beams inorder to achieve load equalization. This system could be expanded toutilize a 3rd order truck but is considered too complex and unnecessaryfor a landing gear application.

(b) Load Equalization--Transverse Direction

Note the horizontal pivot in FIG. 3G.

Wheel load equalization (fore and aft) is achieved by the use of primaryand secondary truck beams as shown, e.g., in combinations of wheelsabove 5 (see FIGS. 3E and 3F).

Wheel load equalization (transverse) is achieved by introducing ahorizontal pivot to each axle (see FIG. 3G).

In wheel load equalization a wheel truck for an aircraft landing gearcarries a plurality of wheel sets, each set having a left-hand wheel anda right-hand wheel. The wheels of any given set are free to rotate abouta longitudinal axis so that they will follow transverse ground contoursas the aircraft taxis. Each wheel set, as a whole, can also pivot abouta transverse axis, in order to adaptively follow longitudinal groundcontours. The pivotable mounting arrangement of the wheels to the truckenables all wheels to maintain an equal force contact with the ground,so that one wheel will not be overloaded relative to another.

ADVANTAGES OF MAIN LANDING GEAR SINGLE WHEEL STEERING

1. MULTIPLE STEERING MODES

The arrangement herein before discussed of FIG. 1 can be incorporatedfor use in multiple wheeled gears as shown in FIGS. 4,5,6,9 and 10. Thedirectional control of each wheel is achieved by electronic control ofthe hydraulic directional valves of the wheels.

Steering arrangements for steering a 4 wheeled truck are shown in FIG.4A, 4B and 4C while steering a 6 wheeled truck is shown (moving to theright) in sequenced steps of FIGS. 5A, 5B and 5C.

Steering arrangements for an 8 wheeled truck are shown in FIGS. 8A, 8B,8C and 8D.

FIG. 9A, Band C shows how the present single wheeled system can beutilized to offset the effect of a side drift landing. The angle of yawis measured by any means (e.g., radar, lazer inertial control) and fedas an electrical signal to hydraulic directional control valves toobtain the required position of all wheels.

FIG. 10 is included merely for purposes of further understanding andshows an improbable situation but one which if it was at all practicalcould save landing gear weight by the near elimination of pivotingloads.

2. REDUCED MOVEMENT ARM

The reduced movement arm is a result of the reduced distance from thekingpin centerline and tire centerline as compared to distancescurrently utilized in e.g., a Boeing type 747 body gear (of FIG. 6)where: ##EQU1##

The example for main gear single wheel steering is then as shown in FIG.7 where: ##EQU2##

ADVANTAGES OF THE PRESENT MAIN LANDING GEAR SINGLE WHEEL STEERINGEMBODIMENTS INCLUDE

1. The use of the "Ackermann Steering System" on aircraft landing gear,i.e., the method of minimizing the loads normally transferred to thesteering actuators.

2. The use of a steering system which permits individual wheel movementin different directions as required.

3. The feature of the steering angle being twice that of the singlewheel angular movement. This is achieved by steering leading andtrailing twin axles in opposite directions. (See FIGS. 4C, 5C and 8A, 8Band 8C.)

4. The ability of all wheels on all gears to be directionally controlledfor all side drive landing using the main gear steering system. (SeeFIGS. 9A, and 9D.)

5. Possible positioning of wheels for relieving pivoting loads.

STEERING PERFORMANCE WITH VERTICAL STEERING PINS ANGULATED WITH RESPECTTO THE VERTICAL AXIS OF THE LANDING GEAR

By utilizing the vertical load on the gear, a rotational motion aroundthe center of the steering pin can be achieved. The amount and directionof this motion is dependent upon the amount and direction of the tilt ofthe pin.

Irrespective of the direction of steering, it is required that thismotion (induced by the vertical load) always causes the wheel to want toreturn to a straight ahead attitude.

In the case of rear axle steering shown in FIGS. 11A and 11B, the tileof pivot pin 100 would be zero when viewed in the fore/aft direction(FIG. 11B), but when viewed from the side (FIG. 11A), pin 100 tilts sothat the top of the pinpoints forward and consequently the lower end ofthe pin points rearward. This would apply also to the front axle shouldthat be steered.

The tilting for single wheel steering (king pin steering) shown in FIGS.12A and 12B is quite different as far as direction is concerned. Becauseeach pin 110, 112 controls one wheel 210, 212 respectively (see FIG.12B), pins 110 and 112 will be vertical when viewed from the sideelevation (see FIG. 12A), and tilted when observed in the fore/aft planeof FIG. 12B. In order for the wheel to feel resistance to the movementas the steering angle increases (and consequently seeks to return to thestraight ahead mode), the top of the pivot pin would lean inboard(towards the truck center line), and the lower part of the pin wouldobviously lean outboard (away from the truck center line). This is truefor both left 210 and right 212 hand wheels as seen in FIG. 12B.

What is claimed is:
 1. In combination in an aircraft:a main landing geartruck including a wheel and brake assembly and having single wheel (KingPin) steering; a pivot pin controlling one wheel; and said pivot pinarranged vertically with respect to the vertical axis of the mainlanding gear truck when viewed from side elevation and tilted withrespect to the vertical axis of the landing gear when observed in thefore and aft plane thereby reducing the potential energy of said wheeland brake assembly during a hardover condition following a potentiallinkage failure.
 2. In combination in the landing gear of anaircraft;the top of a pivot pin leaning inboard toward a truck centerline and the lower part of said pivot pin leaning outboard away fromsaid truck center line; said pivot pin providing an increasingresistance to the rotational motion of the wheel around the said pivotpin center line in the event of either electrical, hydraulic, pneumatic,or mechanical failure of the steering system; and said resistance to therotational motion of the wheel continuing beyond the steering range ofthe system until the wheel contacts the nearest mechanical stop.
 3. Incombination in an aircraft landing gear:a pivot pin (KingPin)controlling the revolution of one wheel, and said pivot pin (KingPin) arranged vertically with respect to the vertical axis of thelanding gear when viewed from side elevation, and said pivot pin (KingPin) tilted with respect to the vertical axis of the landing gear whenobserved in the fore and aft plane, and the top of said pivot pin (KingPin) leaning inboard toward a landing gear truck center line, and thelower part of the said pivot pin (King Pin) leaning outboard away fromsaid truck center line, and said pivot pin (King Pin) providingincreasing resistance to the rotational motion of the said wheel aroundsaid center line in the event of the said mechanical failure, and as aresult of said pivot pin (King Pin) tilting, and said resistance to therotational motion of the said wheel continuing to increase beyond thesteering range of the system, until the wheel contacts the nearestmechanical stop, thereby providing reduction of possible structuraldamage, and said rotational motion providing for activation of a shockabsorbing device between the said wheel and mechanical stop, therebyfurther reducing the possibility of damage.